Single circuit refrigeration appliance

ABSTRACT

A single-circuit refrigeration appliance includes a thermally insulated housing and a refrigerant circuit in which the following are connected in series between a pressure connection and a suction connection of a compressor: a condenser, a first throttle point, a first evaporator that cools a first storage compartment in the housing, a second throttle point, and a second evaporator that cools a second storage compartment in the housing. The second throttle point has an adjustable volume flow rate.

The present invention relates to a single-circuit refrigeration appliance having two storage compartments which can be temperature-controlled independently of one another.

In a single-circuit refrigeration appliance, a compressor, a condenser and the evaporators of typically two storage compartments are connected in series in a refrigerant circuit so that the entire flow of refrigerant circulated by the compressor flows consecutively through both evaporators.

The distribution of the available cooling power to the evaporators of the storage compartments in such a single-circuit refrigeration appliance is typically fixedly predefined by the geometry and arrangement of the evaporators. The share of the individual storage compartments in the overall cooling requirement of the appliance varies however depending on the ambient temperature. If such a refrigeration appliance is operated at a lower ambient temperature than that for which it is optimized, the cooling requirement of the warmer storage compartment reduces proportionally to a greater extent than that of the colder storage compartment, so that if the operation of the compressor is controlled on the basis of the cooling requirement of the warmer storage compartment, the colder storage compartment is no longer cooled sufficiently. If by contrast the compressor operation were controlled on the basis of the cooling requirement of the colder storage compartment, the result would be excessive cooling of the warmer storage compartment. A known solution to this problem is to provide a heater in the warmer storage compartment, which can be switched on during operation in a cold environment, in order to artificially increase the cooling requirement of the warmer storage compartment and thus to ensure a compressor life span which is sufficient to also keep the colder storage compartment at a setpoint temperature. It is obvious that such a heater severely impairs the energy efficiency of the refrigeration appliance.

Dual-circuit refrigeration appliances allow the temperature of two storage compartments of a refrigeration appliance to be regulated independently of one another. With these appliances, the refrigerant pipe comprises two branches, wherein refrigerant can be applied to just one of the two evaporators by way of one of these branches and either the other or both evaporators are supplied in series with refrigerant by way of the other branch. The required branching renders the refrigerant circuit considerably more complicated and results in higher manufacturing costs than with a single-circuit refrigeration appliance.

With no-frost refrigeration appliances, there is the option of controlling the allocation of the cooling power to the storage compartments, by the heat exchange between evaporator and storage compartment being modulated with the aid of a ventilator. The use of ventilators also increases the complexity and manufacturing costs of the appliance; moreover, if the heat exchange between an evaporator and an assigned storage compartment is blocked by switching off the ventilator, said evaporator achieves very low temperatures which likewise affect the energy efficiency of the appliance.

The object of the invention is therefore to create a single-circuit refrigeration appliance, which allows the temperature of two storage compartments to be regulated independently of one another, without having to heat one of the storage compartments for this purpose.

The object is achieved by, in the case of a single-circuit refrigeration appliance having a thermally insulated housing and a refrigerant circuit, to which, between a pressure connection and a suction connection of a compressor, a condenser, a first throttle point, a first evaporator for cooling a first storage compartment formed in the housing, a second throttle point and a second evaporator cooling a second storage compartment formed in the housing are connected in series, the second throttle point having an adjustable volume flow rate. The adjustability of the volume flow rate allows for different pressures to be set in the two evaporators during operation of the compressor, and thus also for different evaporation temperatures of the refrigerant in the two evaporators, depending on the required temperature in the relevant storage compartment.

This solution can be also be used in particular in cold wall appliances and therefore allows for the manufacture of highly energy-efficient and yet cost-effective refrigeration appliances.

A control circuit can be connected to a first temperature sensor arranged on the first storage compartment and to the second throttle point and set up so as to increase the volume flow rate of the second throttle point if cooling is required in the first storage compartment. By increasing the volume flow rate, the pressure of the refrigerant in the first evaporator is reduced and the resulting lower evaporator temperature causes the first storage compartment to be more intensively cooled.

By contrast, the control circuit can be connected to a second temperature sensor arranged on the second storage compartment and set up so as to reduce the volume flow rate of the second throttle point if cooling is required in the second storage compartment. This results in a pressure and thus also a temperature rise on the first evaporator, so that this absorbs less heat from the first storage compartment and a greater share of the available cooling power is available to cool the second storage compartment.

If there is a cooling requirement in both storage compartments, the control circuit should be able to provide more cooling power by increasing the rotational speed of the speed-controlled compressor.

In a maximum opening state, the volume flow rate of the second throttle point may be large in comparison with the volume flow rate of the first throttle point. Therefore, if the second throttle point is in the maximum opening state, the pressure established by the compressor essentially reduces completely at the first throttle point, and the pressure difference between the two evaporators is low so that essentially the same temperatures can be retained in both storage compartments.

Since the pressure in the downstream evaporator cannot be higher than in the upstream first evaporator, the second storage compartment is expediently configured for a lower operating temperature than the first storage compartment. In particular, at least the second storage compartment should be operable as a freezer compartment. The setting of the second throttle point can specify whether the first storage compartment can likewise be used as a freezer compartment or at a higher temperature.

By contrast, at least the first storage compartment should be operable as a normal refrigerator compartment, but this does not rule out its use at lower temperatures, when the second throttle point is set correspondingly.

In order to minimize the operating noise emission by the refrigeration appliance, the second throttle point should comprise a continuous valve. Since different flow cross-sections can constantly be set on such a valve, pressure fluctuations of the refrigerant are minimized during compressor operation, thereby allowing the noise emission of the refrigeration appliance to be kept low overall.

Further features and advantages of the invention will emerge from the description of exemplary embodiments below, with reference to the appended figures, in which:

FIG. 1 shows a schematic representation of the refrigerant circuit of an inventive refrigeration appliance; and

FIG. 2 shows a schematic sectional view through the housing of the refrigeration appliance.

The refrigerant circuit shown in FIG. 1 comprises a speed-controlled compressor 1 with a pressure connection 2 and a suction connection 3. A refrigerant pipe 4 coming from the pressure connection 2 runs in the circulation direction of the refrigerant, firstly via a condenser 5 and a first throttle point 6, here, as standard, realized as a capillary line, to a first evaporator 7. A second, adjustable throttle point 8 is disposed between an outlet connection of the evaporator 7 and an inlet connection of a second evaporator 9. An outlet connection of the evaporator 9 is connected to the suction connection 3 of the compressor 1.

Two temperature sensors 10, 11 are arranged in storage compartments 12, 13 cooled by the evaporators 7 or 9 and connected to a control unit 14, which, on the basis of the temperatures detected by the temperature sensors 10, 11, controls the rotational speed of the compressor 1 and the volume flow rate of the throttle point 8.

In a first operating mode, the control unit 14 continuously compares the temperatures detected by the temperature sensors 10, 11 with setpoint temperatures for the storage compartments 12, 13 which can be set in the typical manner by a user. If the temperature detected in one of the storage compartments 12, 13 significantly exceeds the set setpoint temperature by more than a predetermined value ε, the control unit 14 determines that cooling of the relevant storage compartment is required. This determination remains in existence until the temperature measured in the relevant compartment drops by more than ε to below the setpoint temperature of the relevant compartment.

If, for instance, a cooling requirement is determined in the storage compartment 12, and not in the storage compartment 13, the control unit 14 then increases the volume flow rate of the throttle point 8 by a predetermined increment, thereby causing the pressure drop to reduce at the throttle point 8 and to increase at the throttle point 6. The pressure in the evaporator 7 reduces, thus the boiling temperature of the refrigerant in the evaporator 7 also reduces and the storage compartment 12 is cooled more intensively. Since the power of the compressor 1 is not changed, the cooling power available on the evaporator 9 reduces in exchange.

The increment can be fixedly predetermined or specified by the control unit 14 in proportion to the deviation of the measured temperature from the setpoint temperature of the relevant storage compartment. If a temperature drop is determined a few minutes after adjusting the throttle point 8, the adjustment of the throttle point 8 is clearly sufficient; if no temperature drop is determined, then the volume flow rate is incremented again.

If the storage compartment 13 heats up as a result and its temperature exceeds the setpoint value for this compartment by more than c, the control unit 14 determines that cooling is required in the storage compartment 13. This determination also remains in existence until the temperature in the storage compartment 13 falls by at least c to below the setpoint value.

If cooling is required in the storage compartment 13, but not in the storage compartment 12, the control unit 14 responds by reducing the volume flow rate of the throttle point 8. As a result, the pressure increases in the evaporator 7 and drops in the evaporator 9. Consequently, the evaporation temperature in evaporator 7 increases and less heat is absorbed from storage compartment 12, so that a larger share of the refrigerant reaches the evaporator 9 in the liquid state. Therefore, at the expense of cooling the storage compartment 12, there is more cooling power available to cool the storage compartment 13.

If the rotational speed of the compressor 1 is sufficient overall to keep both compartments 12, 13 at their setpoint temperatures, the phases of intensively cooling compartment 12 and of intensively cooling compartment 13 thus alternate. If longer time intervals exist in which neither compartment 12 nor compartment 13 has a cooling requirement, the power of the compressor 1 is greater than is needed to cool the compartments 12, 13 and in this case the rotational speed of the compressor 1 slows down and is decremented in small steps in order to find a setting value at which the power of the compressor 1 corresponds as precisely as possible to the cooling requirement of the compartments 12, 13.

A simultaneous cooling requirement in both compartments 12, 13 is an indication that the power of the compressor 1 is not sufficient to keep the compartments 12, 13 at the setpoint temperature, therefore, in such a case the control unit 14 increments the rotational speed of the compressor 1 slowly and in steps until there is no longer a cooling requirement in one of the storage compartments 12, 13.

Under stationary conditions, the afore-described hysteresis when determining the existence or non-existence of a cooling requirement leads to each of the storage compartments 12, 13 tending to have a phase-offset cooling requirement. The compressor 1 can therefore work very uniformly, with a rotational speed which changes rarely and only by way of a few steps. Minor changes to the volume flow rate on the throttle point 8 are sufficient to allocate the cooling power to the storage compartments 12, 13. On account of the continuous operation, the temperatures of both evaporators 7, 9 can be kept close to the setpoint temperature of the corresponding storage compartment 12 or 13 in each case, which allows for a highly energy-efficient operation. By the throttle point 8 being formed by a continuous valve, the flow cross-section of which can assume numerous positions while stationary that correspond to the volume flow rates to be realized in each case, pressure fluctuations in the refrigerant circuit which could result in the emission of operating noises are avoided.

FIG. 2 shows a schematic sectional view through a refrigeration appliance with the refrigerant circuit shown in FIG. 1. As standard, its housing 15 comprises a thermally insulated body 16, in which the two storage compartments 12, 13, each enclosed by a door 17, are formed. The evaporators 7, 10 are each arranged between an inner container 20 of the storage compartments 12, 13 and a surrounding insulation material layer 18. In the case of storage compartment 12, they can only be arranged on a rear wall 19 or, in the case of storage compartment 13, they can also extend to other walls of the inner container 20. The compressor 1 and, in the case shown here, also the condenser 5 and the second throttle point 8 are accommodated in a machine compartment 21 on the rear side of the body 15.

The evaporator 7 positioned upstream in the refrigerant circuit is also the evaporator of the upper storage compartment 12 here, so that the circulation direction of the liquid refrigerant through the evaporators 7, 9 essentially runs from the top down. Since the pressure in the upstream evaporator 7 can never be lower than in the downstream evaporator 9, storage compartment 12 can be used as a normal refrigerator compartment and storage compartment 13 can be used a freezer compartment, but not vice versa.

A second operating mode can be set on the control unit 14, in which the throttle point 8 is always held in a maximum flow cross-section state, so that the pressure difference between the two evaporators 7, 9 is negligible with respect to that at the throttle point 6. In this operating state, depending on the setting of the power of the compressor 1, both storage compartments 12, 13 can be operated with the same setpoint temperature, in particular as a normal refrigerator compartment or as a freezer compartment.

REFERENCE CHARACTERS

-   1 compressor -   2 pressure connection -   3 suction connection -   4 refrigerant pipe -   5 condenser -   6 first throttle point -   7 first evaporator -   8 second throttle point -   9 second evaporator -   10 temperature sensor -   11 temperature sensor -   12 storage compartment -   13 storage compartment -   14 control unit -   15 body -   16 door -   17 door -   18 insulation material layer -   19 rear wall -   20 inner container -   21 machine compartment 

1-9. (canceled)
 10. A single-circuit refrigeration appliance, comprising: a thermally insulated housing; a first storage compartment and a second storage compartment formed in said housing; and a refrigerant circuit including a compressor having a pressure connection and a suction connection and the following connected in series between said pressure connection and said suction connection: a condenser, a first throttle point, a first evaporator cooling said first storage compartment, a second throttle point having an adjustable volume flow rate, and a second evaporator cooling said second storage compartment.
 11. The single-circuit refrigeration appliance according to claim 10, wherein said evaporators are cold wall evaporators.
 12. The single-circuit refrigeration appliance according to claim 10, which further comprises: a first temperature sensor disposed in said first storage compartment; and a control circuit connected to said first temperature sensor and configured to increase said volume flow rate of said second throttle point if cooling is required in said first storage compartment.
 13. The single-circuit refrigeration appliance according to claim 10, which further comprises: a second temperature sensor disposed in said second storage compartment; and a control circuit connected to said second temperature sensor and configured to reduce said volume flow rate of said second throttle point if cooling is required in said second storage compartment.
 14. The single-circuit refrigeration appliance according to claim 10, wherein: said compressor is a speed-controlled compressor having a rotational speed; and a control circuit is configured to increase said rotational speed of said speed-controlled compressor if cooling is required in said first and second storage compartments.
 15. The single-circuit refrigeration appliance according to claim 10, wherein said first throttle point has a volume flow rate, and said volume flow rate of said second throttle point in a maximum opening state is larger than said volume flow rate of said first throttle point.
 16. The single-circuit refrigeration appliance according to claim 10, wherein said second throttle point has a continuous valve.
 17. The single-circuit refrigeration appliance according to claim 10, wherein at least said second storage compartment is operable as a freezer compartment.
 18. The single-circuit refrigeration appliance according to claim 10, wherein at least said first storage compartment is operable as a normal refrigerator compartment. 